Method of oscillatory bonding

ABSTRACT

Methods and apparatus are disclosed for the bonding together of two similarly shaped articles of similar thermoplastic material utilizing oscillatory motion between the two articles to generate frictional heat therein sufficient to form an hermetic seal therebetween.

BACKGROUND OF THE INVENTION

The present invention relates generally to the bonding together of twosimilarly shaped portions of thermoplastic articles and moreparticularly involves friction welding of upper and lower containersections to provide a single hermetically welded container.

The prior art discloses a method of welding container sections togetherto form a single container, which method is directed to cylindricallyshaped thermoplastic containers which are rotated at high speeds againsteach other to generate by friction the heat necessary to bond the twosections together. This prior art method is commonly referred to asspin-welding and is disclosed in such patents as U.S. Pat. No.3,297,504, U.S. Pat. Reissue No. 29,448, and U.S. Pat. No. 3,499,068.

While the prior art method of spin-welding is advantageous over suchmethods as chemical bonding, cementing, and thermal bonding by meanssuch as laser, electon beam, radio wave, and electrical means, it offersan disadvantage in that it is restricted to 20 cylindrical joints.Obviously two non-cylindrical container sections could not besuccessfully spin-welded because of their lack of surfaces which wouldmaintain contact during relative rotary motion between them.

The present invention overcomes the disadvantage of rotary spin-weldingby providing methods and apparatus for friction welding thermoplasticcontainers having non-cylindrical joinder sections as well as beingapplicable also to cylindrical sections. The present invention utilizesoscillatory motion, rather than rotary motion, between the two sectionsto be joined to provide the friction for generating the heat of bondingbetween the two sections.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 are cross-sectional side views of three different types ofcontainer joints which can be joined utilizing the present invention;

FIG. 4 is a partial side view of an oscillatory welding apparatus forlow-frequency welding;

FIG. 5 is a schematic view of a rotary air joint for use with theapparatus of FIG. 4;

FIG. 6 is a partial side view of an oscillatory welding apparatus forhigh-frequency welding;

FIG. 7 is a schematic diagram of the rotary joint to provide air andelectrical power to the apparatus of FIG. 6.

FIG. 8 is a schematic top view of the rotary infeed and exit system forthe oscillatory welding apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a modification and improvement over theapparatus disclosed in U.S. Pat. Nos. 3,499,068 and Re. 29,448, whichpatents are herein incorporated by reference in their entirety. For easeof description the present invention will be described with reference toonly one station of a multi-station system such as the multi-stationsystems disclosed in the above-mentioned incorporated patents. Exceptfor the modifications disclosed with respect to the single describedstation, the remainder of the container-forming system of this inventionis substantially the same as that of the incorporated patents.

Referring now to FIG. 4, the single station 10 of the bonding system 11is shown in side elevational view. The single station is typical of theother stations contained on the multiple station rotary system. Thestation comprises an upper carrier assembly 12 mounted by rollers and anupper cam head 13. The lower carrier assembly 14 is mounted in a lowercam assembly 15 by roller follower means 16. Upper assembly 12 ismounted in cam head 13 by roller follower 17.

Upper cam head 13 generally comprises a substantially circular verticalcam plate 18 having formed therein a peripheral cam groove 19. Camgroove 19 passes circumferentially around cam head 13 and is arranged toreceive roller follower 17 in relatively close-fitting engagementtherein. Cam channel 19 has vertical fluctuations such as shown at 20for providing controlled vertical movement of carrier assembly 10 as itrotates about cam head 13.

Likewise lower cam assembly 15 contains a peripheral cam channel 21encircling the generally circular shaped cam head 15 and arranged toreceive cam follower 16 rotatably therein. Cam channel 21 likewise hasvertical fluctuations for providing vertical movement of lower assembly14 with respect to upper assembly 10.

Lower assembly 14 generally comprises a vertical spindle mount 22 towhich is attached a lower tool 23 for receiving and tightly clamping thelower portion of the container to be bonded. Tool 23 preferably has aninternal cavity facing upward shaped generally to conform to the shapeof the lower container portion to be bonded. Futhermore, tool 23 hasconventional means such as a vacuum system for selectively gripping thelower container portion therein.

Upper carrier head 12 is joined by shaft 24 to cam follower 17. Camfollower 17 is rotatably mounted on shaft 24. Also mounted on carrierhead 12 is an air oscillator 25 acting through a pin joint 26 to anoscillatory diaphram 27 which in turn is fixedly attached to carrierhead 12. Oscillator 25 has a slidable shaft 28 extending downwardlytherefrom to which is connected an upper tool spindle 29 having an uppertool 30 attached thereto. Tool spindle 29 passes through air bearing 31mounted in a bearing housing 32 which is fixedly attached to carrierhead 12. Air bearing 31 allows slidable vertical movement betweenspindle 29 and carrier assembly 10. Upper tool 30 has conventional meanssuch as vacuum means for tightly gripping the upper portion of thecontainer to be joined to the lower portion held in tool 23. An airsupply source 33 provides air to bearing 31, a second air supply source34 provides air to oscillator 25, and a third air supply 35 provides airto diaphram 27. Oscillatory diaphram 27 is connected to oscillator 25 toprovide amplitude adjustment of the oscillatory motion generatedtherein.

In typical operation, a pair of upper and lower container portions aredenested from a stack thereof by a separate denesting assembly (notshown) and rotated through the various conveying systems associated withthe aforementioned incorporated patented structures such that a bottomportion is secured within tool 23 and an upper portion held in uppertool 30. The movement of carrier 12 and carrier 14 around the circularcam heads 13 and 15 provides vertical movement between tools 23 and 30bringing the container sections into close proximity. When the carrierassemblies 12 and 14, which traverse circularly around cam heads 13 and15 as a single unit, have reached a predetermined point with respect tocam grooves 19 and 21, tools 23 and 30 will have moved into theirclosest position thus bringing the upper and lower container sectionsinto conjoining relationship. Simultaneously with the joining of theupper and lower container sections, air is supplied via tube 34 to theair oscillator 25 thus providing a low frequency oscillation of theupper container held in tool 30 within the lower container clamped intool 23 to sufficiently generate enough heat between the two containersections to provide an hermetic bonding therebetween. The number ofoscillations necessary to provide bonding depend upon various parametersincluding the type of plastic utilized in the containers, as well as thecontainer size and the frequency and amplitude of the oscillations.These will be known to the operator prior to adjusting the machinery,and the time and frequency of the oscillations will have been presetsuch that at the moment bonding is beginning, the oscillations will beterminated to allow the container sections to form a good bond. The airoscillator terminates oscillations in the lowermost position such thatthe container sections will be fully joined. Shortly after theoscillations have ceased and bonding, has been achieved, movement of thecarrier assemblies 12 and 14 around cam heads 13 and 15 by means of theengagment of cam followers 16 and 17 in cam grooves 19 and 21 will movethe carrier assemblies vertically apart and allow removal of the bondedcontainer sections. These will then be transported via conventionalmeans away from the bonding assembly.

FIG. 5 is the schematic representation of the rotary air joint to whichair supply tubes 33, 34, and 35 are connected. FIG. 5 illustrates therotary joint 40 having an air supply outlet 41 to connect with diaphramsupply tube 35, a second air supply port 42 connnectable to airoscillator supply tube 34, and a third air supply port 43 connectable toair bearings supply tube 33. As the carrier assemblies 12 and 14 arerotated about their respective cam heads 13 and 15, the air supply ports41-43 communicate with the various supply tubes to supply a properlytimed sufficient quantity of air into the various air actuatedcomponents of the assembly.

Referring now to FIG. 6, the second embodiment of the invention isdisclosed, which embodiment is particularly useful for high frequencyoscillatory bonding of container parts. In this embodiment the carrierassembly of the first embodiment has been replaced by a high frequencycarrier assembly 100. This carrier assembly is mounted on similar camheads 13 and 15 by roller followers 17 and 16. Assembly 100 comprises anupper carrier body 101 and a lower roller body 102. Upper tool body 101has located thereon a mounting bracket 103 which mounts an ultrasonictransducer 104 lying in a vertical plane substantially parallel to camplate 13. Transducer 104, which is electrically operated, is connectedto a power source via electrical connection 105. At the lower end oftransducer 104 is a pin connection 106 connecting an upper spindle 107to the transducer. An air bearing 108 connected to body 101 supportsspindle 107 in vertically slidable orientation. An upper containerretention tool 109 is secured at the lower end of spindle 107. Retainertool 109 preferably has an internal cavity formed in the general shapeof the container top to be welded. The lower assembly 102 comprises alower spindle 110 mounted on carrier block 102 and having a lowercontainer retention tool 111 mounted at the top thereof. Tool 111 has aninternal cavity similarly shaped to the lower portion of the plasticcontainer to be welded. Tools 109 and 111 have conventional means forclamping tightly onto container sections.

In typical operation, the two carrier assemblies comprising a singlestation 100, will be rotated about their respective cam plates 13 and 15with roller followers 17 and 16 engaged in cam grooves 20 and 21. Thisrotary movement and concurrent camming action around plates 13 and 15 bythe station assembly results in a vertical movement of the upper andlower spindles toward and away from each other. At one point in thisoperation, while the upper and lower tools 109 and 111 are spaced apart,a plastic container top will be located in tool 109 and a plasticcontainer bottom will be located in tool 111 by means conventional inthe art. Additional movement of the cam followers in cam channels servesto translate the upper and lower spindles toward each other until theupper and lower plastic container sections are brought into matingcontact. At this point in time the transducer will be supplied withelectric power through lead 105 causing a very high frequencyoscillation of the upper spindle 107 to occur, which in turn oscillatesthe upper plastic container with respect to the lower plastic container,setting up friction forces which result in a high heat generation and asubsequent welding of the upper and lower container sections together toform an hermetic seal. The continuous movement of the assembly aroundthe cam plates then spreads the upper and lower spindles apart, allowingremoval of the welded container unit from the upper and lower tools byknown means.

FIG. 7 is a schematic diagram of a rotary joint located near the centrallongitudinal axis of the total assembly. In FIG. 7 the circuits for theelectrical supply are indicated at 112 and 113. An air supply isconnected to a rotary air joint 114 to provide air to the bearing 108.In addition, conventional means such as vacuum or mechanical means canbe provided in the tool holders 109 and 111 to secure the plasticcontainers therein during the oscillatory welding stage.

FIG. 8 is a plan schematic view of a feed system 200 for the bondingassembly. The feed system comprises a rotary infeed such as starwheel201, providing delivery of containers into the various stations 10, andthe exit wheel 202 comprising a starwheel for removing the bondedcontainers after the welding process has been accomplished. Themulti-station oscillatory welding system 11 is shown having tenindividual welding stations 10 illustrated.

FIGS. 1-3 illustrate various joints that can be welded utilizing thepresent assembly and rigid plastic container sections. FIG. 1illustrates a partial cross-sectional view of upper container 301 whichis fused to a lower container section 302. This type of joint isnormally referred to as a "compressive shear" joint. The outer diameterof the lower section 302 is a few thousandths inch larger than the innerdiameter of the upper section 301. Section 301 is forced over section302 to provide an air-tight fit and the oscillation between the twosections provides, through the heat of friction, a sufficient melting ofthe thermoplastic material to form a tight hermetic bond therebetween.FIG. 2 represents a partial cross-sectional side view of a fusion jointbetween two plastic articles, such as two sections of a container, or acontainer wall and a container bottom. This type of joint is generallyreferred to as an "energy director" joint. In this joint the side wall401 of a container section is oscillated between upwardly extendingflanges 402 and 403 of a plastic bottom section 404. The wall section401 preferrably has a slight interference fit in between upper flanges402 and 403 to provide sufficient friction heat to bond the bottomsection to the wall 401.

FIG. 3 illustrates an alternate embodiment of the clamping function ofthe upper tool 501 of a container section 502. The container section 502is to be friction welded to the lower container section 503. In thisembodiment a wedge shaped clamp 504 connected to a first cam tracklocated on upper cam plate 13 grips the container member 502. Member 504is wedge shaped into a diverging orientation at the lower end and aslidable tightening ring 505 is located around the outer periphery ofthe wedge shaped clamping member. A second cam track located on theupper cam plate directs the vertical movement of clamping member 505downward on wedge member 504 to provide an inward compression ofcontainer member 502. The timing of the first and second cam tracks onthe upper cam member is such that member 505 is lowered on member 504 tocompress container member 502 down upon container member 503 aftercontainer member 503 has just entered the barrel flange area 502a.Thereupon member 505 is moved downward to compress clamp 504 andcontainer 502 into compression on container 503. After the downwardclamping motion of outer member 505, oscillations are generated in theentire upper assembly to oscillate member 502 over 503 and providesufficient heat of friction to bond the two container sections together.

Thus a welding system for friction welding plastic containers has beendisclosed which is particularly advantageous for the joining of twothermoplastic container sections which are of a non-circularcross-sectional configuration. The present invention utilizesoscillatory axial motion as opposed to the conventional rotary motion ofprior art spin-welders. The oscillatory motion being a translationalmotion rather than a rotating motion allows containers of almost anycross-sectional configuration to be friction welded together. Thepresent invention discloses embodiments for low frequency oscillatorywelding of plastic articles, and apparatus for high frequencyoscillatory welding apparatus.

Although a specific embodiment of the present invention has beendescribed in the detailed description above, the description is notintended to limit the invention to the particular forms or embodimentsdisclosed therein since they are to be recognized as illustrative ratherthan restrictive and it will be obvious to those skilled in the art thatthe invention is not so limited. For example, whereas electricaltransducers and air operated oscillatory apparatus are disclosed forproviding oscillatory welding action, it is clear that other means suchas hydraulic action and mechanical oscillations could be utilized intheir place. Also, whereas the top container portion is oscillated incontact with the bottom container section, it is possible to oscillatethe bottom section instead, or to even oscillate both sections of thecontainer.

The parameters which may be utilized for practicing various embodimentsof the invention include selecting an oscillating frequency in the rangeof around 50 to about 50,000 cycles per second, with one particularpreferred range being from about 120 to about 240 cycles per second. Thepolymers which can advantageously be welded by the present processinclude both amorphous and crystalline organic resins such as styrenes,polystyrenes, propylenes, polypropylenes, acrylonitriles, lexans,polyethylene, high density polyethylene, polyethylene terephthalate, andpolyethylene terephthalate glycol. Thus the invention is declared tocover all changes and modifications of the specific examples of theinvention herein disclosed for purposes of illustration which do notconstitute departures from the spirit and scope of the invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A method of welding atleast two similarly configured themoplastic sections together havingrelatively tight-fitting complementary joinder portions, said methodcomprising:sliding said tight-fitting portions together into telescopicconjoinment; oscillating said portions axially with respect to eachother at a sufficiently rapid rate and for a sufficient period of timeto generate enough heat to melt the areas of contact therebetween; and,bringing said sections into a final desirable position and allowing saidheated areas to cool, thereby welding said sections together.
 2. Themethod of claim 1 wherein said thermoplastic sections are sized toprovide an interference fit therebetween.
 3. The method of claim 1 orclaim 2 wherein said thermoplastic sections are made from organicthermoplastic resins each having melt temperatures relatively close tothe other.
 4. The method of claim 1 or claim 2 wherein saidthermoplastic sections are made from identical organic resins.
 5. Amethod of forming a container from at least two thermoplastic sectionseach having a non-circular cross-sectional configuration which closelymatches the other section, said method comprising:clamping saidcontainer sections into separate holder means providing axial telescopicalignment of the sections with each other; oscillating at least one ofsaid holder means at a sufficiently rapid rate for a sufficient periodof time, while maintaining said sections in telescoped arrangement, togenerate enough heat to melt the contact areas therebetween; bringingsaid telescoped sections to a final preselected desirable position withrespect to each other while still partially melted; and, allowing saidheated areas to cool sufficiently to solidify said heated thermoplasticareas.
 6. The method of claim 5 wherein at least one of said sections isan organic polymer selected from the group consisting of styrenes,polystyrenes, propylenes, polypropylenes, acrylonitriles, lexans,polyethylene, high density polyethylene, polyethylene terephthalate, andpolyethylene terephthalate glycol.
 7. The method of claim 5 or claim 6wherein said thermoplastic sections are made of thermoplastic materialshaving melt temperatures within about 30° F. of each other.
 8. Themethod of claim 5 or claim 6 wherein said oscillating step is performedat a frequency of from about 120 to about 240 cycles per second.
 9. Themethod of claim 5 or claim 6 wherein said oscillating step is performedat a frequency of from about 20,000 to about 40,000 cycles per second.10. The method of claim 5 or claim 6 wherein said oscillating step isperformed at a frequency of from about 50 cycles per second to about50,000 cycles per second.
 11. The method of claim 5 wherein saidthermoplastic sections are made from at least one amorphous organicresin.
 12. The method of claim 5 wherein said thermoplastic sections aremade from at least one crystalline organic resin.